1. Field of the Invention
This invention relates to a two-stroke internal combustion engine, especially such an engine with a pressure-sensitive wall contained within a chamber for isolating the crankcase from the combustion chamber.
2. Description of the Related Art
In a conventional two-stroke internal combustion engine, the vacuum caused by a piston moving away from the crankcase draws a mixture of fuel, air, and oil into the crankcase through a one-way valve or timed induction mechanism such as a piston port or rotary valve. Increased pressure produced by the piston moving toward the crankcase forces the mixture of fuel, air, and oil into the piston cylinder on the side of the piston away from the crankcase and, therefore, into the combustion chamber, which is at the portion of the piston cylinder that is the most distant from the crankcase, because such carbureted fuel cannot escape through the one-way valve or a now closed induction mechanism.
The crankcase is used as a compressor. This requires the crankcase to have relatively close tolerances between the crank and the crankcase, itself. It is also required that the crankcase be sealed. These factors isolate the crankcase from any lubrication that may be in other parts of the engine. Therefore, a secondary lubrication system is necessary. However, any oil in the crankcase would readily be pushed into the combustion chamber. Therefore, to minimize the oil that is pushed into the combustion chamber, oil is continuously added to the crankcase, but only in small quantities. In conventional two-stroke engines this is accomplished either by oil injection or by utilizing fuel which has been pre-mixed with a suitable quantity of oil. But no matter how the lubrication is achieved, oil will be introduced into the combustion chamber and combusted. And during the combustion process, such oil creates considerable smoke and other pollution.
Additionally, when a traditional two-stroke internal combustion engine compresses the mixture of fuel, air, and oil (before the transfer ports open), some of the fuel and oil can go past the piston skirt and into the exhaust port unburned. This adds to hyrocarbon pollution of the atmosphere and limits the attainable crankcase pressure.
U.S. Pat. No. 4,248,185 of Eric Jaulmes employs a membrane 7 in the crankcase pump 1 of a two-cycle engine, but the sole purpose of that membrane 7 is to divide the crankcase pump 1 into two chambers 8 and 9. Chamber 8 contains the crankshaft 6 and the connecting rod 4 and would, therefore, also contain oil for lubrication. Since carbureted air passes through chamber 8 on its way to the piston cylinder 2, oil (whether pre-mixed with fuel or injected into the crankcase) would thereby be introduced into the piston cylinder 2. Pure air passes through chamber 9 to reach the piston cylinder 2; but because of the oil-containing carbureted air, the membrane 7 does not isolate the piston cylinder 2 from the oil in the crankcase. In the alternate embodiment of FIGS. 7 through 9, the carbureted air passes through chamber 9; and pure air goes through chamber 8. Thus, as explained in lines 25 through 28 of column 4, it is necessary to provide separate lubrication, i.e., lubrication could not be accomplished by oil pre-mixed with the fuel. The oil that would be separately added for lubrication would then travel with the air to the piston cylinder 2.
U.S. Pat. No. 5,291,866 of David R. Kosa applies to a Pulse Charger 40 which supplies air from the crankcase 24 of a four-cycle internal combustion engine to the intake system 18 of that engine. It is asserted that a baffle 120 between the crankcase 24 and the pulse charger 40 xe2x80x9caids in keeping any liquid from enteringxe2x80x9d the pulse charger and that an xe2x80x9cadditional oil separator 140 . . . may also be included in order to separate crankcase oil from the pulsed air charge prior to the pulsed air charge entering carburetor or fuel injection system 52 [which carburetor or fuel injection system 52 is placed between the pulse charger 40 and the intake system 18]. Oil separator 140 can be of the centrifugal type, the baffle type or any other type of separator known in the art.xe2x80x9d The baffle 120 and oil separator 140, however, attempt to remove oil from air which such oil has already infiltrated rather than precluding such oil from ever entering the air.
The supercharger in U.S. Pat. No. 3,672,172 of Gary L. Hammond appears to operate in a fashion rather similar to that of U.S. Pat. No. 5,291,866. xe2x80x9cTo avoid any undesired entrainment of oil in the supercharging air, an air-oil separator such as, for example, louvered baffle, wire mesh screen, loose packed metal shavings or the like, or combinations thereof, is employed [between the crankcase 26 or 122 and the inlet valve 12 or intake port 104]. The separator should not unduly restrict airflow but should trap entrained oil.xe2x80x9d In attempting to remove oil from air which such oil has already infiltrated rather than precluding such oil from ever entering the air, the devices of U.S. Pat. Nos. 5,291,866 and 3,672,172 do, however, necessarily limit airflow.
Some two-stroke internal combustion engines avoid introducing oil into the carbureted air by not using the crankcase as a pump. Instead, these engines utilize superchargers, which are heavy, expensive, and inefficient because the blower is always turning and putting a load on the engine even when there is no demand from the engine for fuel or air, i.e., when the transfer ports are closed.
The present invention utilizes the pressure and vacuum cycles created within the crankcase of a crankcase compression two-stroke internal combustion engine to force air into the piston cylinder, also termed the combustion chamber, of the engine. A flexible diaphragm, bellows, or floating piston is, though, utilized to isolate the air that travels to the combustion chamber from the crankcase. Therefore, no oil ever enters the combustion chamber.
As the piston moves away from the crankcase, a vacuum is created within the crankcase. This draws the flexible diaphragm, bellows, or floating piston within an isolation chamber toward the crankcase, creating a vacuum on the side of the diaphragm, bellows, or floating piston away from the crankcase and drawing a mixture of fuel and air (or plain air if either a fuel injection system that injects fuel into the combustion chamber is utilized or a charge former is between the isolation chamber and the transfer port) through a one-way valve or timed induction mechanism into the isolation chamber on the side of the diaphragm, bellows, or floating piston that is away from the crankcase.
When the piston moves toward the crankcase, the increased pressure pushes the diaphragm, bellows, or floating piston in the isolation chamber away from the crankcase. Because the mixture of fuel and air or pure air on the side of the diaphragm away from the crankcase cannot escape through the one-way valve or timed induction mechanism, such mixture of fuel and air or pure air is forced into the piston cylinder and, therefore, into the combustion chamber.
Such mixture of fuel and air or pure air is, therefore, pumped into the combustion chamber without ever being exposed to oil that lubricates the crankcase and without the use of a supercharger.
Preferably, the piston is designed with a full-length skirt around the entire perimeter of the piston and with at least one ring around the piston. This ring is placed so that it is always between all ports and the crankcase in order to preclude oil that is either maintained within and/or circulated through the crankcase from passing between the piston and the wall of the piston cylinder and thereby entering the exhaust port or the transfer port. (Oil in the exhaust port would be heated to such an extent that it would smoke or be pushed into the surrounding environment; oil in the transfer port would be pushed into the combustion chamber and create smoke during combustion which would then be exhausted to the surrounding environment.)